The main principle of the automated blood analyzers is to get the quantity (count) of different blood components (parameters) in the peripheral blood samples. Additionally, in case of Sysmex KX-21 blood analyzer, the work performance includes also 3-part differential white blood cells (WBC) count represents eight parameters of the complete blood count (CBC). Extremely important to mention here that many of the analyzed information about the main blood corpuscular are provided in a graphical forms called histograms. Remarkably, any abnormal results in the investigated blood parameters due to multi different factors such as red blood cell fragments, platelets clumps, cold agglutinins, giant platelets and many other factors will appear in an abnormal histograms and flags. These abnormalities in values and histograms or flags appeared need to be interpreted and adjusted depending on extensive knowledge of the analytic performance of the analyser and the clinical significance of the results they provide.